COOS BAY — Construction of Wastewater Treatment Plant No. 2 is nearing completion, with workers at the site gearing up for 30 days of clean water testing in the coming weeks.

“We are in a startup phase right now. The electrical for the most part is all online. We’ve functionally tested probably 90 percent of the process equipment out there,” Mortenson Project Manager Bob Sanguinetti said.

Wastewater Treatment Plant No.2 project engineer Janette Kerbo explains how wastewater moves through the plant's system, and into a large basi…

At the end of this month, the project will enter into a second level of functional testing, where the automated controls of the plant will be tested.

The treatment plant basins were tested a couple of weeks ago using clean water, but it is important to note that this was not part the required 30-day test period. Water was run through manually to test for leaks.

“Right now, if we want to test a pump, somebody goes to the power panel and turns a switch there to manually turn that pump off and on. So it’s not running on its own like it will be as a final system,” Coos Bay’s Project Engineer Janette Kerbo said.

Initial testing on the plant checks to make sure that there is proper power going to each of the units, and that each piece of the whole system works.

Coos Bay expects the new treatment plant to cost $23 million.

The old wastewater treatment plant is what’s called a Conventional Activated Sludge Plant.

“It has a series of basins. Flow comes into a primary clarifier where some of the solids are pulled off, then it goes into an aeration basin, and then to a secondary clarifier. It then goes to a chlorine contact chamber. You have to have four separate basins, and you’re either using gravity flow or pumping to each basin.” Kerbo said.

The new plant is a Sequencing Batch Collector system, which means three of the processes that occur in a Conventional Activated Sludge Plant all take place in one basin. It also uses ultraviolet light to disinfect the water instead of chlorine.

Wastewater Treatment Plant No 2 project manager Bob Sanguinetti opens a hatch to show the new plant's Effluent Pump Station, which is where th…

Kerbo said that treating the water with UV lights is not only cheaper but also safer for both the treatment plant workers and the environment. In a UV disinfection system, workers are not exposed to chlorine, and water does not have to be de-chlorinated before it’s put into the bay.

Construction on the project has run fairly smooth. At the beginning of the plant’s construction, work crews found that they were working on top of unsuitable soil for the facility which had to be replaced with rock.

“One of the biggest issues we’ve had as things started gearing up was procurement of materials. Sometimes people tell you it’ll be 10 weeks, but it ends up being 14,” Sanguinetti said.

Wastewater Treatment Plant No. 2 is on schedule, and may be testing with raw sewage as soon as late October.

Once the new plant is up and running, the old plant will be decommissioned and disassembled over a period of about six weeks.